The woman paid for her own drink, then asked to pay for the drink of the person behind her in the drive-through. That person returned the favor and paid for the person behind, and so did that person, until the employees at the St. Petersburg Starbucks on Tyrone Boulevard began a tally on green laminated paper near the drive-through window.

By 1:30 p.m., the chain had reached 260 customers.

People ordered a drink at the speaker. When they pulled through to the next window, the barista, Vu Nguyen, 29, leaned through and said with a smile that their drinks had already been paid for by the person in front of them. Would they like to return the favor?

"It makes your day better, I think," said Lexie Kane, 17, of St. Petersburg, who ordered an iced coffee.

Tim Burnside, 19, had visited in the morning and paid it forward. He returned later to see whether it was still going on. Seeing that it was, he ordered a second chai tea.

"It's nice just to do a random act of kindness for someone you don't know," said Burnside, also of St. Petersburg.

Some said the simple act connected them to all of the others in line before them. Others said they didn't want to be the jerk to end it.

The baristas inside began to think of what they might do if it lasted until 10 p.m., when the Starbucks closed. Perhaps they could put the final amount on a gift card and continue the next day? They tallied 378 people by early evening.

Then at 6 p.m., customer No. 379 — a woman in a white Jeep Commander — pulled into the drive-through and ordered a regular coffee.

Nguyen leaned out the window. He told her about the chain that had begun that morning. Would she like to participate? The woman declined, saying she just wanted to pay for her $2.25 drink and not someone else's.

Nguyen said it appeared the woman didn't understand the concept of paying it forward.